1. Field of the Invention
The present invention generally relates to a hermetically sealed rotary compressor and, more particularly, to the hermetically sealed rotary compressor of a type suited for use in a refrigerator, an air-conditioner or the like for compressing a gas-phase refrigerant.
2. Description of the Prior Art
The hermetically sealed rotary compressor is well known in the art, an example of which is shown in FIGS. 24 and 25 in longitudinal and transverse sectional representations, respectively, for discussion of the prior art believed to be relevant to the present invention.
The hermetically sealed rotary compressor shown in FIGS. 24 and 25 includes a generally cylindrical sealed vessel 1 tightly closed at its opposite ends and accommodating therein an electric motor 3 comprised of a stator and a rotor. This sealed vessel 1 also accommodates therein a compressor mechanism 4 positioned beneath the electric motor 3 and adapted to be driven by the electric motor 3. During the drive of the compressor mechanism 4, a refrigerant introduced into the compressor mechanism from a gas-liquid separator 14 through an intake port 15 by way of a connecting tube 25 is compressed. The resultant compressed refrigerant is discharged into the sealed vessel through an outlet port and then therefrom to a refrigerating circuit through a discharge tube 16.
The compressor mechanism 4 of the prior art rotary compressor comprises, as best shown in FIGS. 24 and 25, a crankshaft 5 adapted to be driven by the electric motor 3 and having its upper and lower ends rotatably received by upper and lower bearing plates 9 and 10, respectively, a generally intermediate portion of said crankshaft 5 extending through a cylinder 6 fixed in position inside the sealed vessel 1. An eccentric cam 7 is fixedly mounted on, or otherwise formed integrally with, a portion of the crankshaft 5 situated within the cylinder 6 for rotation together therewith. A ring-shaped piston 8 is operatively positioned between an inner wall surface of the cylinder 6 and an outer peripheral surface of the eccentric cam 7 and will, during the drive of the crankshaft 5, undergo a planetary motion.
As best shown in FIG. 25, the cylinder 6 has a radial groove 11 defined therein so as to extend in a direction radially thereof, and a slidable radial vane 12 is accommodated within this radial groove 11 for movement within the radial groove 11 in a direction close towards and away from the crankshaft 5. This slidable radial vane 12 is normally biased by a biasing spring 19 in one direction with a radially inward end thereof held in sliding contact with an outer peripheral surface of the ring-shaped piston 8, thereby dividing the volume of the cylinder 6 into volumetrically variable, low and high pressure chambers 17 and 18 that are defined respectively on leading and trailing sides of the slidable radial vane 12 with respect to the direction of rotation of the crankshaft 5.
According to the prior art hermetically sealed rotary compressor shown in FIGS. 24 and 25, a gas-phase refrigerant is, during the planetary motion of the ring-shaped piston 8 accompanying an eccentric rotation of the eccentric cam 7 rigid with the crankshaft 8, sucked into the low pressure chamber 17 through the intake port 15 and then compressed before it is discharged through the outlet port (not shown). In order to facilitate a sliding motion of the ring-shaped piston 8 relative to the inner wall surface of the cylinder 6 and the radial inner end of the slidable radial vane 12 and also a sliding motion of the radial vane 12 within the radial groove 11, a quantity of lubricating oil is accommodated within the sealed vessel 1 as indicated by 2 in FIG. 24. The lubricating oil 2 is sucked up by an oil pump 13 operatively disposed below the lower end of the crankshaft 5 to oil various sliding elements within the compressor mechanism 4.
Of the various sliding elements used in the compressor mechanism 4, the slidable radial vane 12 when noticeably worn out causes a detrimental problem. As is well known to those skilled in the art, the slidable radial vane 12 is frictionally engaged not only with the ring-shaped piston 8, but also with side surfaces defining the radial groove 11 in the cylinder 6. Specifically, by the biasing force of the biasing spring 19 and a back pressure acting on a radial outer end of the slidable radial vane 12, the radial inner end of the slidable radial vane 12 is constantly held in frictional engagement with the ring-shaped piston 8 and, also, by the effect of a pressure difference between the low and high pressure chambers 17 and 18, opposite side surfaces of the slidable radial vane 12 are alternately held in frictional engagement with the corresponding side surfaces of the radial groove 11. Unlike other sliding elements such as, for example, the crankshaft and its bearing mechanism, the slidable radial vane 12 is not lubricated by a lubricating oil supplied directly by the oil pump 13, but is lubricated by an oil component, contained in the refrigerant being compressed, and/or an oil leaking from bearing rollers. The quantity of the oil available from the refrigerant being compressed and leaking from the bearing rollers is indeed insufficient for lubricating the slidable radial vane 12 and its surrounding parts satisfactorily. In addition, considering that the refrigerant when compressed is in elevated temperature, the slidable radial vane 12 in contact with the refrigerant being compressed is therefore heated and is therefore susceptible to an accelerated frictional wear.
In order to eliminate the above discussed problems, the Japanese Laid-open Patent Publication No. 4-203286 suggests the use of such an oil injector mechanism as shown in FIG. 26. The refrigerating circuit disclosed in this publication includes a condenser 38 fluid-connected with an expansion valve 39 through a connecting tube 40 having a by-pass passage 41 branched off therefrom for injecting an oil and a liquid-phase refrigerant into the low pressure chamber 17. This by-pass passage 41 has an oil reservoir 42 disposed thereon, and oil within the oil reservoir 42 is introduced into the low pressure chamber 17 by the effect of a developed pressure difference to thereby lubricate the ring-shaped piston 8 and the slidable radial vane 12. Since the mere supply of oil will result in reduction in efficiency because of ingress of heated oil into the cylinder, the oil is mixed with the liquid-phase refrigerant to prevent the interior of the cylinder from being heated.
For the refrigerant used in the refrigerating system including the hermetically sealed rotary compressor, dichlorodifluoromethane (hereinafter referred to as "CFC 12") or hydrochlorofluoromethane (hereinafter referred to as "HCFC 22") is generally used. On the other hand, the lubricant oil filled in the compressor mechanism 5 is generally either a mineral oil of naphthene or that of paraffin having a solubility with CFC 12 or HCFC 22.
Since the refrigerant and the lubricating oil circulate directly within the sealed vessel 1, the various component parts of the compressor mechanism 4 must have a sufficient resistance to wear.
Apart from the above, it has come to be recognized that emission of Freon such as used as the refrigerant into the atmosphere does not only seriously deplete the ozone layer, but brings about global ecological damage. In view of this, an international agreement has been made to step by step freeze for some years ahead and eventually abolish the production of CFC 12 and HCFC 22. Under these circumstances, as a substitute refrigerant, 1,1,2-tetrafluoroethane (hereinafter referred to as "HFC 134a"), 1,1 difluoroethane (hereinafter referred to as "HFC 152a" and hydrodifluoromethane (hereinafter referred to as "HFC 32") or a mixture thereof have been developed.
While the substitute refrigerant such as HFCs 134a, 152a and 32 is less likely to result in depletion of the ozone layer, it lacks a solubility with such a mineral lubricant as hitherto used in combination with the CFC 12 or HCFC 22. For this reason, where the substitute refrigerant is to be used in the refrigerating system, attempts have been made to use such a lubricant oil of ether, ester or fluorine family which has a compatibility with the substitute refrigerant.
However, where a combination of any one of the HFCs 134a, 152a and 32 in place of any of the CFC 12 and HCFC 22 with either polyalkylene glycol oil or polyester oil having a compatibility with such substitute refrigerant is used in the refrigerant compressor, it has been found that the resistance to frictional wear of such metallic material as FC25, special cast iron, sintered alloy and stainless steel used for sliding elements in the refrigerant compressor tends to be lowered and, therefore, the refrigerant compressor cannot be operated stably for a long period of time. This is because of the following reasons.
So long as the conventional CFC 12 or HCFC 22 is used as the refrigerant, chlorine atoms contained in the conventional refrigerant react with Fe atoms contained in the metal matrix to form a film of ferric chloride that is excellent in resistance to frictional wear. However, in the case of the substitute refrigerant such as HFC 134a, HFC 152a or HFC 32, no chlorine atom exist in this compound and, therefore, no lubricating film such as a film of ferric chloride is formed, accompanied by a reduction in lubricating action.
In addition, while the conventional mineral oil used as a lubricant contains a cyclic compound and has therefore a relatively high capability of forming an oil film, the lubricant oil compatible with the substitute refrigerant is composed mainly of a chain compound and is therefore unable to form a required oil film under severe sliding conditions, accompanied by an accelerated reduction in resistance to frictional wear.
As discussed above, the refrigerant compressor operable with the substitute refrigerant and the lubricant oil compatible with this substitute refrigerant is often placed under severe sliding conditions not only during a high load drive, but also during a normal drive and, therefore, the frictional wear of the vane and rollers has come to be highlighted.
According to the solution suggested in the previously discussed publication with reference to FIG. 26 in which an oil injector is used to supply a relatively great amount of lubricant oil to the vane and rollers in an attempt to eliminate the above discussed problems, there is a problem in that the refrigerating system tends to be complicated and costly.
Mere connection of the oil reservoir with the low pressure chamber such as employed in the previously discussed publication brings about an additional problem in that a high temperature oil tends to flow into a low temperature chamber to superheat the refrigerant being sucked, accompanied by reduction in efficiency of the compressor.